feat(body_mesh): Add body mesh separator module with edge dissolution

- Add body_mesh submodule with VRM_OT_separate_non_skin_faces operator
- Add VRM_PT_body_mesh_separator panel for UI integration
- Add utility functions for mesh operations and edge dissolution logic
- Add comprehensive edge dissolution configuration files for all body parts (head, torso, arms, legs, hands) with UV coordinates
- Add test utilities for validating mesh separation operations
- Add .gitignore to exclude Python cache files and test artifacts
- Register body_mesh module in editor package initialization
- Update registration.py to include new body mesh components

editor/body_mesh/test_utils.py

@@ -0,0 +1,60 @@
+# SPDX-License-Identifier: MIT OR GPL-3.0-or-later
+"""
+Property-based tests for body_mesh utility functions.
+
+Feature: vrm-body-mesh-separator
+"""
+from hypothesis import given, settings
+from hypothesis import strategies as st
+
+from .utils import generate_unique_name, is_skin_material
+
+
+class TestIsSkinMaterial:
+    """
+    Property 2: 材质分类正确性
+    *For any* 材质名称字符串，`is_skin_material`函数应该返回True当且仅当该名称包含"SKIN"子字符串（不区分大小写）。
+    **Validates: Requirements 2.2, 2.3**
+    """
+
+    @given(st.text())
+    @settings(max_examples=100)
+    def test_skin_material_classification_property(self, material_name: str) -> None:
+        """
+        Feature: vrm-body-mesh-separator, Property 2: 材质分类正确性
+        For any material name string, is_skin_material returns True
+        if and only if the name contains "SKIN" (case-insensitive).
+        """
+        result = is_skin_material(material_name)
+        expected = "SKIN" in material_name.upper()
+        assert result == expected, (
+            f"is_skin_material('{material_name}') returned {result}, "
+            f"expected {expected}"
+        )
+
+
+class TestGenerateUniqueName:
+    """
+    Property 6: 唯一命名保证
+    *For any* 基础名称和已存在名称集合，`generate_unique_name`返回的名称不应该在已存在名称集合中。
+    **Validates: Requirements 4.2**
+    """
+
+    @given(
+        st.text(min_size=1, max_size=50).filter(lambda x: x.strip()),
+        st.sets(st.text(min_size=1, max_size=50), max_size=20),
+    )
+    @settings(max_examples=100)
+    def test_unique_name_generation_property(
+        self, base_name: str, existing_names: set[str]
+    ) -> None:
+        """
+        Feature: vrm-body-mesh-separator, Property 6: 唯一命名保证
+        For any base name and set of existing names, generate_unique_name
+        returns a name that is not in the existing names set.
+        """
+        result = generate_unique_name(base_name, existing_names)
+        assert result not in existing_names, (
+            f"generate_unique_name('{base_name}', {existing_names}) "
+            f"returned '{result}' which is in existing_names"
+        )